A microwave oven is a kitchen appliance used to heat food through microwaves. Similar kitchen appliance further includes optical oven.
Metal objects, folded and irregular foils in particular, may be dangerous for a microwave oven, because metal may reflect microwaves inside the microwave oven and generate sparks that may ignite food and components of the microwave oven. In the related art, a warning label is placed on a microwave oven to prompt a user not to place metal contains or objects in the microwave oven. However, since this warning mechanism relies on consciousness of users, accidents may still happen when children or aged users unaware of the danger make use microwave oven without supervision.